The invention relates to a pumping tube. More particularly, the invention relates to the pumping tube used for pumping and filling a flat display panel of the plasma display panel type.
Plasma panels are flat display screens in which the displayed image consists of a set of light discharge points. The light discharges are produced in a gas contained between two insulating tiles, generally made of glass. Each discharge point is generated by a discharge cell defined by an intersection between arrays of electrodes carried by at least one of the tiles. The gas contained between the two tiles is generally a gas mixture which emits visible or invisible radiation when a discharge is produced. To obtain sufficient light emission, it is necessary to have a gas or gas mixture as pure as possible.
Pumping tubes are used for evacuating and then filling plasma display panels. Conventionally, the pumping tubes are made of glass so as to be sealed onto one tile of the panel, this tile having been provided beforehand with a hole. The pumping tube is mounted after the two tiles forming the panel have been joined together.
FIG. 1 shows a pumping tube 1 according to the prior art, which comprises a tubular part 2, for carrying out the pumping, and a plane part 3 intended to bear on one face of the tile of the panel.
To be able to seal the pumping tube 1 onto the panel, a bead 4 of glass paste is placed on the plane part 3, as shown in FIG. 2. The glass paste is a mixture consisting of a glass frit and an organic resin.
After the bead 4 has been deposited, the pumping tube 1 is positioned on the rear tile 5 of the panel and held in place by means of a clip 6, as shown in FIG. 3. The pumping tube 1 is positioned so that it faces a hole 7.
The panel is then heated to a temperature of between 400xc2x0 C. and 550xc2x0 C. so as to melt the glass frit and completely burn off the resin of the paste forming the bead 4.
After localized heating, the bead 4 is converted into an impermeable seal 8. FIG. 4 shows an ideal case of a seal for the pumping tube 1 facing the hole 7. Unfortunately, in reality, many problems arise when positioning the pumping tube 1 and when producing the seal 8. Thus, one or more of the defects shown in FIG. 5 may be encountered.
A first defect is an axial offset 9 between the hole 7 and the pumping tube 1. The axial offset has the effect of reducing the pumping area. This defect occurs when positioning the clip 6.
A second defect is an angular offset 10 with respect to the perpendicular. The angular offset 10 causes non-uniform flattening of the sealing bead, which is manifested in a sealing problem.
A third defect consists of runs 11 of sealing material in the hole 7. This defect is magnified by the angular offset. The main drawback of the runs is a reduction in the pumping orifice and therefore an increase in the pumping time.
Most of these defects may be minimized by greater and expensive precision in positioning the various elements involved in placing the pumping tube 1 on the tile 5.
The invention proposes to remedy the various problems mentioned by reducing the precision needed for mounting the pumping tube. The invention proposes a pumping tube shape which makes it possible, on the one hand, to guide the pumping tube when positioning the latter on the tile and when producing the seal by heating and, on the other hand, to prevent runs inside the pumping hole. Moreover, the pumping tube of the invention makes it possible to produce an almost ideally distributed homogeneous seal, thereby ensuring that the latter seals reliably.
The subject of the invention is a pumping tube for a flat display panel, which pumping tube comprises a plane part intended to bear on an external plane of a tile of the said panel, in order to be sealed thereto, and comprises a tubular part which extends perpendicular to the plane part, the said tubular part being intended to fit into a hole in the tile.
The invention also relates to a plasma display panel comprising two tiles bonded together and forming a cavity, one of the two tiles being provided with a hole making it possible to create a vacuum in the cavity and then to fill the cavity with a gas, and a pumping tube comprising a plane part sealed around the hole, which pumping tube comprises a tubular part which extends perpendicular to the plane part, the said tubular part being inside the hole.